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        <p>对于任何一门知识体系，一定有一个最小基本单位，基本概念，其他的概念或是规矩都是基于这几个基本的东西在玩花样。对于这个很基本的分析问题的方法，混沌大学的李善友老师还起来一个非常高大上的名字叫做“唯一性原理”，有点故弄玄虚，其实叫啥无所谓，面对同样一份原始数据，如果你有相关的知识，你就能将数据切的更细，那就能看到更多东西。</p>
<p>先列举下Baseband的几个基本单位：</p>
<h2 id="1-Piconet"><a href="#1-Piconet" class="headerlink" title="1. Piconet"></a>1. Piconet</h2><p>  跟其他网络技术一样，蓝牙也有自己的网络。网上把这个单词翻译成微网。在蓝牙设备没有跟其他蓝牙设备连线的时候，它自己属于一个piconet。当有连线后，piconet里有两种角色：master 和 slave。发起连线的一方是master，被连接的一方是slave。slave会以master的时钟为参照，以625us为时间单位，与master进行数据收发。每一个piconet里，一个master最多有7个slave。<br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/Spec.Vol1.BluetoothBasic/BREDR_Topology.png" alt="Piconet" title="PicoNet"></p>
<h2 id="2-Mode"><a href="#2-Mode" class="headerlink" title="2. Mode"></a>2. Mode</h2><p>  这里的Mode其实对应的是Modem，数据编码不同，那Modem就不同，传输数据的速度也不同。</p>
<h3 id="2-1-Basic-Rate：最基本的一种模式，采用BPSK，传输速率是-1Mb-s。"><a href="#2-1-Basic-Rate：最基本的一种模式，采用BPSK，传输速率是-1Mb-s。" class="headerlink" title="2.1 Basic Rate：最基本的一种模式，采用BPSK，传输速率是 1Mb/s。"></a>2.1 Basic Rate：最基本的一种模式，采用BPSK，传输速率是 1Mb/s。</h3><h3 id="2-2-Enhanced-Data-Rate：增强模式，传输速率是-2Mb-s-（π-4-DQPSK）或-3Mb-s（8DPSK），这种模式有两种编码。"><a href="#2-2-Enhanced-Data-Rate：增强模式，传输速率是-2Mb-s-（π-4-DQPSK）或-3Mb-s（8DPSK），这种模式有两种编码。" class="headerlink" title="2.2 Enhanced Data Rate：增强模式，传输速率是 2Mb/s （π/4-DQPSK）或 3Mb/s（8DPSK），这种模式有两种编码。"></a>2.2 Enhanced Data Rate：增强模式，传输速率是 2Mb/s （π/4-DQPSK）或 3Mb/s（8DPSK），这种模式有两种编码。</h3><h2 id="3-BT-clock"><a href="#3-BT-clock" class="headerlink" title="3. BT clock"></a>3. BT clock</h2><p>  Clock是蓝牙通信最最基础的一个概念，clock定义了通信的时空范围，定义了这个Piconet时空的坐标系，只有在同一个坐标系里，网络内的各个角色才能相互了解对方的时间线，才知道什么时候发包，什么时候收包。<br>  BT clock是个28bit的计数器，每tick一次是312.5us，所以总共有 (2^28 -1)个tick，算一下大约是(2^28-1)*312.5us/10^6/3600 = 23.3个小时后clock会翻转。<br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/BaseBand_BluetoothClock.png" alt="BT Clock" title="BT Clock"><br>  针对clock有几个概念也要知道下：</p>
<blockquote>
<p>CLK0, 312.5us，是一个tick<br>CLK1, 625us, 是一个slot<br>CLK2, 1.25ms, 是一个frame（做一次TX 和 RX）<br>CLK12, 1.28s.<br>  Clock的精确度要求为 +/-250ppm 和 +/-20ppm</p>
</blockquote>
<h2 id="4-BT-地址"><a href="#4-BT-地址" class="headerlink" title="4. BT 地址"></a>4. BT 地址</h2><p>  蓝牙地址有48bit，需要跟IEEE去购买。<br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/BluetoothAddr.png" alt="BDA" title="BD Address"><br>  LAP中有64个：0x9E8B00-0x9E8B3F是用来做inquiry的。0x9E8B000 是用来做 General inquiry，余下的63个是用来做Dedicate inquiry。当保留LAP被使用的时候，UAP会是0x00，Default Check Initialization。</p>
<h2 id="5-Access-Code"><a href="#5-Access-Code" class="headerlink" title="5. Access Code"></a>5. Access Code</h2><p>  所有的蓝牙数据包都以access code为开头，所有的access code是从LAP生出来的。access code是为了告诉对方，数据包来了，该做准备了，而接收方也可以根据access code来确定这包数据是不是属于自己的。</p>
<blockquote>
<p>device access code (DAC)<br>channel access code (CAC)<br>Inquiry access code (IAC)</p>
<blockquote>
<p>IAC 又分为 GIAC 和 DIAC</p>
</blockquote>
</blockquote>
<h2 id="6-Physical-Channel（信道）"><a href="#6-Physical-Channel（信道）" class="headerlink" title="6. Physical Channel（信道）"></a>6. Physical Channel（信道）</h2><p>  蓝牙有79个信道,每个信道2M<br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/baseband_79_Channels.png" alt="79 Channels" title="bluetooth channels"><br>  Spec总共有定义如下5种channel</p>
<blockquote>
<p>Basic piconet physical channel<br>Adapted piconet physical channel<br>Page scan physical channel<br>Inquiry scan physical channel<br>Synchronization scan physical channel</p>
</blockquote>
<h3 id="6-1-Basic-piconet-physical-channel"><a href="#6-1-Basic-piconet-physical-channel" class="headerlink" title="6.1 Basic piconet physical channel"></a>6.1 Basic piconet physical channel</h3><p>   在建立连线后，Slave会以Mater的clock为准。Master和Slave以一个slot为单位进行Tx和Rx，Master在clock为偶数时发包，Slave在clock为偶数时收包，如下面的两张图。<br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/BaseBand_Master_TXRX_Cycle.png" alt="MasterCycle" title="Master Tx/Rx Cycle"><br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband_Slave_RxTx_cycle.png" alt="Slave Cyle" title="Slave Rx/Tx Cycle"><br>   为了处理time sliping，定义uncertainty window来增加Rx的时候收到包的几率，Slave可以加大自己的Rx时间uncertainty window来提高收到包的几率。<br>   如果在250ms内等不到Master的包，那Slave就只能认为是短线了。</p>
<h3 id="6-2-Adapted-piconet-phycial-channel"><a href="#6-2-Adapted-piconet-phycial-channel" class="headerlink" title="6.2 Adapted piconet phycial channel"></a>6.2 Adapted piconet phycial channel</h3><p>   用到的channel个数可能会少于79个，不过至少会是20个。</p>
<h3 id="6-4-Page-scan-phycial-channel"><a href="#6-4-Page-scan-phycial-channel" class="headerlink" title="6.4 Page scan phycial channel"></a>6.4 Page scan phycial channel</h3><p>   在Paging的时候，Master会发送paging message（就是ID packets），这个时候的跳频速度是 3200 hops/s，在Tx的slot内会打两次包，在Rx的Slot内也会收两次Slave的回应。<br>   Slave在收到Master的paging messagse后的625us会回一个slave reponse packet。Master在收到这个reponse packet的后面的那个Tx slock再发一个master page reponse packet。<br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-PageScanRxTxCycle.png" alt="Page Scan Channel" title="PageScan"><br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-PageScanInFirstHalfSlot.png" alt="Page Scan at 1st half slot" title="1st half slot"><br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-PageScanIn2ndHalfSlot.png" alt="Page at 2nd half slot" title="2nd half slot"></p>
<h3 id="6-5-Inquiry-Scan-Physical-channel"><a href="#6-5-Inquiry-Scan-Physical-channel" class="headerlink" title="6.5 Inquiry Scan Physical channel"></a>6.5 Inquiry Scan Physical channel</h3><p>  在Inquiry的时候，Master会一直发送inquiry mesasge，带上GIAC 或 DIAC。<br>   <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-InquiryScanAt1stHalfSlot.png" alt="Inquiry Scan" title="Inquiry Scan at 1st half"><br>   <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-InquiryScanAt2ndHalfSlot.png" alt="Inquiry Scan 2" title="Inquiry Scan at 2nd half"></p>
<h2 id="7-HOP-Seletion-（跳频）"><a href="#7-HOP-Seletion-（跳频）" class="headerlink" title="7. HOP Seletion （跳频）"></a>7. HOP Seletion （跳频）</h2><p>  据说跳频的理论模型还是个<a href="https://www.sohu.com/a/144238786_693721">演员</a>发明的。</p>
<h3 id="7-1-Selection-Kernel"><a href="#7-1-Selection-Kernel" class="headerlink" title="7.1 Selection Kernel"></a>7.1 Selection Kernel</h3><p>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-SelectionKernelOfHoppingSystem.png" alt="Selection Kernel" title="Selection Kernel"><br>  <img src="https://wnnwoo.oss-cn-chengdu.aliyuncs.com/BluetoothBaseband/Baseband-SelectionKernelHopSystemControlWord.png" alt="Control word" title="Control word"></p>

      
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